This invention relates to a method and apparatus for heating an elongated space or a location containing an elongated heater. More particularly, the invention relates to an electrical resistance heater for heating an elongated space at rates which are different at different locations along the space and heater.
It is known to be beneficial to use elongated heaters such as well heaters, for heating intervals of subterranean earth formations, pipe interiors, or other elongated spaces. In various situations, it is desirable to heat such spaces at relatively high temperatures for relatively long times. Beneficial results obtained by such heating may include pyrolizing oil shale formations, coking oil to consolidate unconsolidated reservoir formations, coking oil to form electrically conductive carbonized zones capable of operating as electrodes within a reservoir formation, thermally displacing hydrocarbons derived from oils or tars into production locations, preventing formation of hydrates, precipitates, or the like in fluids which are being produced from wells and/or transmitted through pipes, or the like.
Prior processes for heating elongated spaces are contained in patents such as the following: U.S. Pat. No. 2,732,195 on heating intervals of from 20 to 30 meters long within subterranean oil shales at temperatures of 500.degree. to 1000.degree. C. using electrical resistance heaters; U.S. Pat. No. 2,781,851 by G. A. Smith, on using a mineral insulated copper sheathed low resistance electrical heater cable containing three copper conductors at temperatures up to about 250.degree. C. for preventing hydrate formation during gas production; U.S. Pat. No. 3,104,705 on consolidating reservoir sand by thermally coking the reservoir hydrocarbons within them; U.S. Pat. No. 3,131,763 on an electrical heater for initiating an underground combustion within a reservoir; U.S. Pat. No. 4,415,034 on forming a coked oil electrode within an oil-containing reservoir formation by heating the reservoir fluids at a temperature of about 1500.degree. F. for as long as 12 months.